1. Field of the Invention
The present invention relates to the fabrication of semiconductor devices. More specifically, the present invention relates to a baking apparatus having a hot plate in a chamber for baking a semiconductor wafer.
2. Description of the Related Art
In general, high density semiconductor devices have miniaturized circuit patterns whose fabrication requires a rigorous management of parameters that influence the size of the miniaturized pattern. In particular, the operating parameters of a photolithography process directly influence the size of the miniaturized pattern. Such a photolithography process includes steps of depositing a photoresist on a wafer, exposing the deposited photoresist to light through a reticle having a pattern to transcribe the pattern of the reticle onto the photoresist, and developing the exposed photoresist to pattern the photoresist.
The developing process, in turn, includes steps of spraying a developing solution onto the wafer so as to remove the exposed portion of the photoresist and leave the non-exposed portion as a pattern, or conversely, to leave the exposed portion as the pattern and eliminate the non-exposed portion. Then, the residual developing solution is removed by spraying pure water onto the wafer. Next, the wafer is subjected to a post bake in which the wafer is baked at constant temperature.
Such a baking process is generally carried out by a baking device having a chamber, and a hot plate e quipped within the chamber. The wafer on which the photoresist was developed is mounted on the hot plate and baked at a constant temperature. The baking device must bake the photoresist uniformly if a fine pattern is to be ultimately formed using the patterned photoresist as an etch mask, for example.
That is, the speed and manner in which the wafer is brought to a constant baking temperature once the wafer enters the chamber, and the degree to which the baking temperature can be maintained during the baking process, directly influence the yield of the semiconductor devices. Therefore, a baking device having a precise temperature control and offering a quick temperature compensation is needed.
In a conventional bake chamber, as shown in FIG. 1, a wafer W is mounted on a hot plate 11 equipped within a chamber 10. Then the wafer W is heated to a constant temperature so as to fix a pattern. This process does not incur any problems in the general cases of forming patterns. However, a CD (Critical Dimension) defect may occur in the case of forming a contact hole having a small diameter or in the case of some photoresists that are especially sensitive to heat.
A present attempt to minimize such problems involves processing the inner surface of a cover 20 that faces the hot plate 11 in an oxide so as to roughen its surface. Roughening the surface of the cover 20 is aimed at scattering the heat from the hot plate 11 to thereby maintain the wafer at a uniform temperature. However, the temperature of the hot plate 11 nonetheless remains non-uniform and is lowest at a central portion thereof. Consequently, the CD of the photoresist pattern at the central region C of the wafer W (FIG. 2) is too low in comparison with the CD of the photoresist pattern at the other regions (T, L, R, F) of the wafer. Thus, the photoresist pattern will produce a defect when used to form a fine pattern in a subsequent process such as an etch process.
Therefore, an object of the present invention is to provide a baking apparatus for manufacturing semiconductor devices, wherein the processing atmosphere can be stabilized in a short time, a CD of a wafer baked in the apparatus will remain relatively uniform, and the baking process can be carried out in a short period of time.
In accordance with an aspect of the present invention, the baking apparatus for manufacturing semiconductor devices comprises a chamber containing a hot plate on which a wafer is to be mounted, a cover covering an upper part of the chamber, and a thin film extending over an inner surface of the cover which increases the rate of formation of a uniform temperature distribution in the chamber. Preferably, the thin film is made of material having a low emissivity (xcex5), preferably in the range of 0.02xcx9c0.05. The inner surface is disposed face-to-face with the hot plate provided in the chamber.
The thin film may be formed discretely from the cover and adhered thereto, or may be produced in-situ on the inner surface of the cover. The surface of the thin film is preferably polished so as to be specular.
In particular, the thin film is made of material that is resistant against corrosion caused by organics. For example, the thin film is of aluminum, brass, copper, aluminum-plated copper, gold or silver.